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Abstract:

A silicate luminescent material and the production method thereof are
provided. The chemical formula of the silicate luminescent material is
Re4-xTbxMgSi3O13, wherein Re is at least one element
selected from the group consisting of Y, Gd, La, Lu and Sc, and
0.05≦x≦1. The silicate luminescent material has a short
afterglow of 2.13 ms, and it can emit strong green light under the vacuum
ultraviolet excitation. Additionally, the silicate luminescent material
has stable physical and chemical properties. The production method for
producing the silicate luminescent material is simple and cost-efficient.

Claims:

1. A silicate luminescent material, wherein the chemical formula of said
silicate luminescent material is Re4-xTbxMgSi3O13,
wherein Re is at least one element selected from Y, Gd, La, Lu and Sc,
and 0.05.ltoreq.x≦1.

2. The silicate luminescent material according to claim 1, wherein Re is
a combination of two or more elements selected from Y, Gd, La, Lu and Sc.

3. The silicate luminescent material according to claim 1, wherein x is
0.1-0.5.

4. A method for producing a silicate luminescent material, comprising the
steps of: providing a source compound of each element according to the
molar ratio defined in the chemical formula
Re4-xTbxMgSi3O13, wherein Re in said chemical formula
is at least one element selected from Y, Gd, La, Lu and Sc, and
0.05.ltoreq.x≦1; mixing the source compounds of the elements;
subjecting the mixture of the source compounds of the elements to a
pre-calcination treatment; subjecting the pre-calcinated product to
calcination under a reducing atmosphere, followed by cooling and then
milling to obtain the silicate luminescent material.

5. The method for producing a silicate luminescent material according to
claim 4, wherein said pre-calcination treatment comprises the process of
pre-calcinating the mixture of the source compounds of the elements in
air for 1-8 hours at a temperature of 1000-1400.degree. C.

6. The method for producing a silicate luminescent material according to
claim 4, wherein said calcination comprises the process of milling the
pre-calcinated product, and calcinating it for 1-8 hours under a reducing
atmosphere at a temperature of 1100-1500.degree. C.

7. The method for producing a silicate luminescent material according to
claim 4, wherein the step of mixing the source compounds of the elements
comprises adding boric acid into the mixture in an amount of 0.5-5 mol %
based on the molar amount of Re4-xTbxMgSi3O13 and
then milling for mixing.

8. The method for producing a silicate luminescent material according to
claim 4, wherein, in the source compounds of the elements, the source
compound of Re is at least one of oxides, carbonates, oxalates and
nitrates thereof, the source compound of Tb is at least one of oxides,
carbonates, oxalates and nitrates thereof, the source compound of
magnesium is at least one of magnesium oxide, magnesium carbonate,
magnesium oxalate and magnesium nitrate, and the source compound of
silicon is silicon dioxide.

9. The method for producing a silicate luminescent material according to
claim 4, wherein the reducing atmosphere is an atmosphere formed by a
mixed gas of nitrogen and hydrogen, carbon monoxide gas or hydrogen.

10. The method for producing a silicate luminescent material according to
claim 4, wherein the temperature of calcination is higher than the
temperature of pre-calcination by 100-350.degree. C.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to the technical field of luminescent
material, particularly to a silicate luminescent material and production
method thereof.

BACKGROUND OF THE INVENTION

[0002] In recent years, with an increasing demand for lighting devices and
display devices in the market, luminescent materials have become one of
the competed hot topics of research and development. So far, a variety of
luminescent materials have been developed and utilized, such as organic
electroluminescent materials, photoluminescent materials, cathode ray
excited luminescent materials, and ultraviolet radiation excited
luminescent materials. These different kinds of luminescent materials can
be applied in corresponding lighting devices, display devices etc,
respectively.

[0003] For example, plasma display panel is a kind of novel direct-view
type image display device following the development of cathode ray tube
and liquid crystal display. Plasma display panel has the advantages of
active emitting, high brightness, large viewing angle, high contrast
ratio, good color reproduction, abundant gray scale and fast response,
and has become an important technology for flat panel display requiring a
large panel and a high definition. The luminescent mechanism of plasma
display panel is as follows: due to the discharge of an inert gas such as
Xe or Xe--He, said inert gas is then turned into a plasma status which
emits vacuum ultraviolet radiations at 147 nm and 172 nm which in turn
excite the fluorescent powder coated on the inner wall to emit lights of
the three primary colors, i.e. red, green and blue. A color display can
be achieved by spatial color mixing and circuit control.

[0004] Currently, Zn2SiO4:Mn2+ is one of the most commonly
used green fluorescent powder in plasma display panel. When excited by
vacuum ultraviolet radiations, Zn2SiO4:Mn2+ exhibits
excellent brightness, excellent deterioration resistance and
fast-to-reach saturated brightness. However, the afterglow period of
Zn2SiO4:Mn2+ is too long, which has an adverse effect on
fast displayed images. Furthermore, the dielectric constant of
Zn2SiO4:Mn2+ is higher than that of the red and blue
fluorescent powders used in plasma display panels, and thus a greater
inducing voltage is required for driving display devices such as plasma
display panel.

[0005] Currently, a novel green fluorescent powder is under study in order
to meet all the requirements of plasma display panels. Such a novel green
fluorescent powder comprises mainly Mn2+ excited aluminate, for
example, BaMgAl10O17:Mn2+ fluorescent powder,
Ba0.9Mg0.6Mn0.16.8Al2O3 green fluorescent powder
and the like. These novel green fluorescent powders have a lower
dielectric constant. However, since Mn2+ is used as the activator,
these novel fluorescent powders still exhibit a relatively long afterglow
period, and the luminescent brightness of these fluorescent powders is
relatively low.

DISCLOSURE OF THE INVENTION

Technical Problems of the Invention

[0006] In this connection, the present invention provides a silicate
luminescent material having a short afterglow period and high luminescent
brightness.

[0007] Furthermore, the present invention provides a method for producing
the silicate luminescent material, which is simple and cost-effective.

Technical Solution of the Invention

[0008] A silicate luminescent material is provided, which has a chemical
formula of Re4-xTbxMgSi3O13, wherein Re is at least
one element selected from Y, Gd, La, Lu, Sc, and 0.05≦x≦1.

[0009] In addition, a method for producing the silicate luminescent
material is provided, said method comprises the steps of:

[0010] providing a source compound of each element according to the molar
ratio defined in the chemical formula
Re4-xTbxMgSi3O13, wherein Re in said chemical formula
is at least one element selected from Y, Gd, La, Lu, Sc, and 0.05x1;

[0011] mixing the source compounds of the elements;

[0012] subjecting the mixture of the source compounds of the elements to a
pre-calcination treatment;

[0013] subjecting the pre-calcinated product to calcination under a
reducing atmosphere, followed by cooling and then milling to obtain the
silicate luminescent material.

The Beneficial Effects of the Invention

[0014] The above-mentioned silicate luminescent material and the
production method thereof possess at least one of the following
advantages.

[0015] (1) The silicate luminescent material has a short afterglow period
of about 2.13 ms, which is much shorter than that of the commercial
Zn2SiO4:Mn2+.

[0016] (2) The silicate luminescent material uses
Re4MgSi3O13 as the matrix, into which Tb ions are doped.
Said matrix exhibits a strong absorption to vacuum ultraviolet
radiations. Due to the activation of Tb ions, the luminescent material
exhibits relatively strong green emission when excited by vacuum
ultraviolet radiations.

[0017] (3) The silicate luminescent material is very stable, and shows no
substantial changes in its properties even after being subjected to
treatments like water immersion, and high-temperature heating, etc.

[0018] (4) The method for producing the silicate luminescent material is
achieved mainly by precalcination and calcinations. The process is simple
and easy to realize the industrialization, and has a broad prospect in
production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described referring to the
drawings and Examples, in which

[0020]FIG. 1 is a flowchart of the method for producing the silicate
luminescent material of the Examples of the present invention;

[0021]FIG. 2 is an emission spectrum of the silicate luminescent material
of Example 6 of the present invention, wherein the excitation wavelength
is 172 nm;

[0022]FIG. 3 is an excitation spectrum of the silicate luminescent
material of Example 6 of the present invention, wherein the monitoring
wavelength is 543 nm;

[0023]FIG. 4 is the fluorescence decay curve of the silicate luminescent
material of Example 6 of the present invention.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0024] In order to make the objects, the technical solutions and the
advantages of the invention more apparent, the present invention will be
further described referring to the drawings and Examples. It should be
understood that the embodiments described herein are merely illustration
of the invention and shall not be construed as limiting the invention.

[0025] The silicate luminescent materials of the examples of the present
invention has a chemical formula of Re4-xTbxMgSi3O13,
wherein Re is at least one element selected from Y, Gd, La, Lu, Sc, and
0.05≦x≦1. Among them, Re may be a combination of two or
more elements selected from Y, Gd, La, Lu, Sc, for example a combination
of Y and Gd, a combination of the four elements, Y, Gd, La, Lu. Through a
combination of these different elements, optical properties of theses
different elements are fully utilized, such that high luminescent
brightness can be achieved. Preferably, x is 0.1-0.5, by which a more
appropriate doping amount of Tb ions can be achieved.

[0026] In the above-mentioned silicate luminescent material,
Re4MgSi3O13 is used as the matrix, into which Tb ions are
doped. Said matrix exhibits a strong absorption to vacuum ultraviolet
radiations. Due to the activation of Tb ions, the luminescent material
exhibits relatively strong green emission when excited by vacuum
ultraviolet radiations, and thus exhibits a relatively high luminescent
brightness. Specifically, when excited by vacuum ultraviolet radiations,
the matrix of the silicate luminescent material absorbs energy, and
transfers it to the Tb ions that act as the emission centers, and green
light emission is generated from Tb ions. The silicate luminescent
material shows relatively strong absorptions at 147 nm and 172 nm,
thereby enhancing its luminous intensity. Accordingly, the silicate
luminescent material is suitable for use in devices such as plasma
display panels.

[0027] The silicate luminescent material has at least the following
advantages:

[0028] (1) The silicate luminescent material has a short afterglow period
of about 2.13 ms, which is much shorter than that of the commercial
Zn2SiO4:Mn2+.

[0029] (2) The silicate luminescent material uses
Re4MgSi3O13 as the matrix, into which Tb ions are doped.
Said matrix exhibits a strong absorption to vacuum ultraviolet
radiations. Due the activation of Tb ions, the luminescent material
exhibits relatively strong green emission when excited by vacuum
ultraviolet radiations.

[0030] (3) The silicate luminescent material is very stable, and shows no
substantial changes in its properties even after being subjected to
treatments like water immersion, and high-temperature heating, etc.

[0031] Refer to FIG. 1, which illustrates a flowchart of the method for
producing the silicate luminescent material of the Examples of the
present invention, said method comprising the following steps:

[0032] S01: providing a source compound of each element according to the
molar ratio defined in the chemical formula
Re4-xTbxMgSi3O13, wherein Re in said chemical formula
is at least one element selected from Y, Gd, La, Lu, Sc, and 0.05x1;

[0033] S02: mixing the source compounds of the elements;

[0034] S03: subjecting the mixture of the source compounds of the elements
to a pre-calcination treatment;

[0035] S04: subjecting the pre-calcinated product to calcination under a
reducing atmosphere, followed by cooling and then milling to obtain the
silicate luminescent material.

[0036] In step S01, in the source compounds of the above elements, the
source compound of Re is preferably at least one of oxides, carbonates,
oxalates and nitrates thereof, the source compound of Tb is preferably at
least one of oxides, carbonates, oxalates and nitrates thereof, the
source compound of magnesium is at least one of magnesium oxide,
magnesium carbonate, magnesium oxalate and magnesium nitrate, the source
compound of silicon is silicon dioxide. Preferably, x is 0.1-0.5.

[0037] Step S02 comprises the processes of adding boric acid into the
mixture of the source compounds of the above elements in an amount of
0.5-5 mol % based on the molar amount of
Re4-xTbxMgSi3O13 or Mg ions and then milling for
mixing. The mixing is specifically preformed as follows: adding boric
acid, followed by sufficiently milling the mixture in a mortar to achieve
homogenous mixing before proceeding to step S03.

[0038] Specifically, step S03 comprises the process of pre-calcinating the
mixture of the source compounds of the elements in air for 1-8 hours at a
temperature of 1000-1400° C. The temperature of pre-calcination is
preferably 1100-1300° C., and the time of pre-calcination is
preferably 2-6 hours.

[0039] Specifically, step S04 comprises the processes of milling the
pre-calcinated product, and calcinating it for 1-8 hours under a reducing
atmosphere at a temperature of 1100-1500° C. The temperature of
calcination is preferably 1250-1400° C., and the time of
calcination is preferably 2-6 hours. More specifically, the temperature
of calcination is higher than that of pre-calcination, for example, by
about 100-350° C., and the total time of pre-calcination and
calcination is preferably 5-12 hours. The reducing atmosphere may be an
atmosphere formed by a mixed gas of nitrogen and hydrogen in a volume
ratio of 95:5, carbon monoxide gas or hydrogen, etc. The precalcination
treatment may also be called a thermal treatment, while the calcinations
treatment may also be called a sintering treatment.

[0040] In addition, the calcinated product may be further milled into
powders, followed by screening to give the fluorescent powder having a
certain particle size.

[0041] In the above production method, the silicate luminescent material
can be readily obtained by the pre-calcination treatment and the
calcination treatment. The entire production process is simple and
cost-effective.

[0042] Different compositions of the silicate luminescent materials and
the production method thereof as well as the properties thereof are
exemplified in the following Examples.

Example 1

Green Fluorescent Powder with the Composition of
Y3.95Tb0.05MgSi3O13

[0043] 1.975 mol of Y2O3, 0.0125 mol of Tb4O7, 1 mol
of MgO and 3 mol of SiO2 are weighed, and 0.005 mol of
H3BO3 is added as the co-flux. These powders are placed in an
agate mortar and sufficiently milled until a homogenous mixture is
obtained. The resulted powder is then transferred to a corundum crucible,
and placed in a muffle furnace for thermal treatment at 1000° C.
for 2 hours, followed by sintering and reducing under a weak reducing
atmosphere of 95% N2+5% H2 in a tube furnace at 1350° C.
for 3 hours, and cooling to room temperature. After milling, a white
product, namely the green fluorescent powder
Y3.95Tb0.05MgSi3O13, is obtained.

Example 2

Green Fluorescent Powder with the Composition of
La3.9Tb0.1MgSi3O13

[0044] 1.95 mol of La2O3, 0.025 mol of Tb4O7, 1 mol of
MgO and 3 mol of SiO2 are weighed, and 0.01 mol of H3BO3
is added as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1200° C. for 5 hours, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1400° C. for 1 hour, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder La3.9Tb0.1MgSi3O13, is obtained.

Example 3

Green Fluorescent Powder with the Composition of
Sc3.5Tb0.5MgSi3O13

[0045] 1.75 mol of Sc2O3, 0.125 mol of Tb4O7, 1 mol of
MgO and 3 mol of SiO2 are weighed, and 0.02 mol of H3BO3
is added as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1300° C. for 1 hour, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1450° C. for 3 hours, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder Sc3.5Tb0.5MgSi3O13, is obtained.

Example 4

Green Fluorescent Powder with the Composition of
Gd3.2Tb0.8MgSi3O13

[0046] 1.6 mol of Gd2O3, 0.2 mol of Tb4O7, 1 mol of
MgO and 3 mol of SiO2 are weighed, and 0.05 mol of H3BO3
is added as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1400° C. for 6 hours, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1500° C. for 1 hour, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder Gd3.2Tb0.8MgSi3O13, is obtained.

Example 5

Green Fluorescent Powder with the Composition of
Lu3TbMgSi3O13

[0047] 1.5 mol of Lu2O3, 0.25 mol of Tb4O7, 1 mol of
MgO and 3 mol of SiO2 are weighed, and 0.05 mol of H3BO3
is added as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1000° C. for 8 hours, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1250° C. for 7 hours, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder Lu3TbMgSi3O13, is obtained.

Example 6

Green Fluorescent Powder with the Composition of
Y3Gd0.5Tb0.5MgSi3O13

[0048] 1.5 mol of Y2O3, 0.25 mol of Gd2O3, 0.125 mol
of Tb4O7, 1 mol of MgO and 3 mol of SiO2 are weighed, and
0.03 mol of H3BO3 is added as the co-flux. These powders are
placed in an agate mortar for sufficient milling until a homogenous
mixture is obtained. The resulted powder is then transferred to a
corundum crucible, and placed in a muffle furnace for thermal treatment
at 1300° C. for 5 hours, followed by sintering and reducing under
a weak reducing atmosphere of 95% N2+5% H2 in a tube furnace at
1400° C. for 3 hours, and cooling to room temperature. After
milling, a white product, namely the green fluorescent powder
Y3Gd0.5Tb0.5MgSi3O13, is obtained.

Example 7

Green Fluorescent Powder with the Composition of
La1.5Sc0.5Lu1.5Tb0.5MgSi3O13

[0049] 0.75 mol of La2O3, 0.25 mol of Sc2O3, 0.75 mol
of Lu2O3, 0.125 mol of Tb4O7, 1 mol of MgCO3 and
3 mol of SiO2 are weighed, and 0.02 mol of H3BO3 is added
as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1400° C. for 1 hour, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1350° C. for 8 hours, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder
La1.5Sc0.5Lu1.5Tb0.5MgSi3O13, is obtained.

Example 8

Green Fluorescent Powder with the Composition of
Y3Lu0.3Tb0.7MgSi3O13

[0050] 3 mol of Y(NO3)3, 0.3 mol of Lu(NO3)3, 0.175
mol of Tb4O7, 1 mol of MgCO3 and 3 mol SiO2 are
weighed, and 0.01 mol of H3BO3 is added as the co-flux. These
powders are placed in an agate mortar for sufficient milling until a
homogenous mixture is obtained. The resulted powder is then transferred
to a corundum crucible, and placed in a muffle furnace for thermal
treatment at 1000° C. for 2 hours, followed by sintering and
reducing under a weak reducing atmosphere of 95% N2+5% H2 in a
tube furnace at 1450° C. for 4 hours, and cooling to room
temperature. After milling, a white product, namely the green fluorescent
powder Y3Lu0.3Tb0.7MgSi3O13, is obtained.

Example 9

Green Fluorescent Powder with the Composition of
YLaGdLu0.5Tb0.5MgSi3O13

[0051] 1 mol of Y(NO3)3, 1 mol of La(NO3)3, 1 mol of
Gd(NO3)3, 0.5 mol of Lu(NO3)3, 0.125 mol of
Tb4O7, 1 mol of MgO and 3 mol of SiO2 are weighed, and
0.008 mol of H3BO3 is added as the co-flux. These powders are
placed in an agate mortar for sufficient milling until a homogenous
mixture is obtained. The resulted powder is then transferred to a
corundum crucible, and placed in a muffle furnace for thermal treatment
at 1100° C. for 3 hours, followed by sintering and reducing under
a weak reducing atmosphere of 95% N2+5% H2 in a tube furnace at
1500° C. for 2 hours, and cooling to room temperature. After
milling, a white product, namely the green fluorescent powder
YLaGdLu0.5Tb0.5MgSi3O13, is obtained.

Example 10

Green Fluorescent Powder with the Composition of
Y3.6Gd0.1Sc0.1Tb0.2MgSi3O13

[0052] 1.8 mol of Y2O3, 0.1 mol of Gd(NO3)3, 0.1 mol
of Sc(NO3)3, 0.05 mol of Tb4O7, 1 mol of MgCO3
and 3 mol of SiO2 are weighed, and 0.05 mol of H3BO3 is
added as the co-flux. These powders are placed in an agate mortar for
sufficient milling until a homogenous mixture is obtained. The resulted
powder is then transferred to a corundum crucible, and placed in a muffle
furnace for thermal treatment at 1200° C. for 6 hours, followed by
sintering and reducing under a weak reducing atmosphere of 95% N2+5%
H2 in a tube furnace at 1350° C. for 8 hours, and cooling to
room temperature. After milling, a white product, namely the green
fluorescent powder
Y3.6Gd0.1Sc0.1Tb0.2MgSi3O13, is obtained.

[0053] In the following, taking the luminescent material
Y3Gd0.5Tb0.5MgSi3O13 of Example 6 as an example,
the excitation spectrum, emission spectrum and fluorescence decay of the
luminescent material are studied in order to illustrate the luminescent
properties of the luminescent material of the present invention.

[0054] Refer to FIG. 2, which shows the emission spectrum of the
luminescent material Y3Gd0.5Tb0.5MgSi3O13
obtained in Example 6 above. As illustrated, the luminescent material
prepared in Example 6 emits under the excitation at 172 nm, and shows a
strong absorption peak at around 543 nm, and the integral intensity of
said emission spectrum is relatively high. Such spectral results
demonstrate relatively strong luminescent properties and relatively high
brightness of the material.

[0055] Refer to FIG. 3, which shows the excitation spectrum of the
luminescent material Y3Gd0.5Tb0.5MgSi3O13
obtained in Example 6 above. As illustrated, the luminescent material
Y3Gd0.5Tb0.5MgSi3O13 shows a relatively strong
absorption to the ultraviolet radiation of around 172 nm, which
demonstrates that the luminescent material has a good absorption in the
range of vacuum ultraviolet wavelengths.

[0056] Refer to FIG. 4, which shows the fluorescence decay curve of the
luminescent material Y3Gd0.5Tb0.5MgSi3O13
obtained in Example 6 above. As illustrated in the figure, the afterglow
period of said material is 2.13 ms, which is much shorter than that of
the commercial green powder currently available. For example, the
afterglow period of the material Zn2SiO4:Mn2+ is 7.1 ms,
which demonstrates that the material of the present invention has a
shorter afterglow period and a shorter fluorescence life time.

[0057] From the test results of the luminescent properties of the
luminescent material of Example 6, it can be seen that the silicate
luminescent material has a short afterglow period of about 2.13 ms which
is much lower than that of the commercial Zn2SiO4:Mn2+,
and exhibits a relatively strong green emission when excited by vacuum
ultraviolet radiations. In addition, the silicate luminescent material
has stable physical and chemical properties which show no substantial
changes even after being subjected to treatments like water immersion and
high-temperature heating. In the method for producing the silicate
luminescent material, the silicate luminescent material can be readily
obtained by pre-calcination and calcinations. Therefore, the method is
simple and cost-effective and has a broad prospect in production.

[0058] Described above are merely preferred embodiments of the present
invention, and are not intended to limit the present invention. Any
modification, equivalent replacement and improvement made without
departing from the spirit and principle of the present invention shall be
encompassed in the protection scope of the present invention.